The present invention generally pertains to the field of wireless broadband communication. More particularly, the present invention is related to a method and system for wireless broadband communication using clustered networks of receivers/transmitters which coherently repeat a signal to a downstream receiver.
Wireless communication systems are requiring ever-increasing bandwidths. This is due to an increase in both the number of customers and the proliferation of high bit rate services. Consequently, vendors such as Internet service providers require higher capacity networks to meet consumer demand for faster service. Frequently, such services are provided in urban areas. However, wireless transmission in such an environment may present problems.
One conventional method of wireless transmission of a signal is far field beam forming. In this conventional system, the base station has a phased array antenna. It is possible to transmit to multiple users on the same frequency and at the same time by placing the nulls correctly. For example, the transmission is sent such that the null of one user""s signal appears at the peak of another user""s signal.
That system works acceptably in a free space environment. However, in a scattering environment it is difficult to maintain a coherent beam. Therefore, this conventional system does not work well in urban environments where buildings scatter the transmitted signal and force the signal into multiple paths.
Another conventional system uses multiple transmitters located around the destination receiver, for example, to the north, south, east, and west. The destination receiver has multiple antennas which may be used to select the desired signal or reject an undesired (interference) signal. For example, two antennas may be used to combine a signal coming from the east with one coming from the south. Alternatively, one antenna is used to receive the desired signal, while another rejects an undesired signal. Unfortunately, this system requires that each receiver have multiple antennas. Furthermore, to be able to selectively reject a signal, a free-space environment is needed. In a scattering environment, the undesired interference signal cannot be detected well enough to reject.
Still another problem is that certain nodes may be at a location for which reception is poor. For example, even though it is near the basestation, the node may be physically located near a wall which blocks reception.
Another problem of some conventional systems is that they are subject to selective frequency fading. For example, if an object such as a truck interferes with the signal, even though some frequencies get through, selective frequencies may fade. Consequently, signal reception is impaired.
Thus, a need has arisen for a method and system for wireless broadband communication suitable for a scattering environment. A still further need exists for a method and system not requiring multiple antennas per receiving station to receive a signal. An even further need exists for such a method and system which is scaleable and suitable for multiple users at high bit rates. A still further need exists for such a method and system which has better fading characteristics than conventional systems described above and can reach stations at poor reception sites.
The present invention provides for a method and system suitable for wireless transmission in a scattering environment. The present invention does not require multiple antennas per receiving station to receive a signal. The present invention provides for a method and system which is scaleable and suitable for multiple users at high bit rates. The present invention has better fading characteristics than conventional systems and can reach stations at poor reception sites. The present invention minimizes selective frequency fading using spatial and frequency transmitter diversity.
A system and method for wireless broadband transmission in a scattering environment using a network of coherent repeaters is disclosed. In one embodiment, the system comprises groups of nodes. The nodes in a group are capable of broadcasting to each other and of beamforming to another group of nodes. First, a basestation broadcasts a number of signals at the same frequency and time. Each signal comprises a desired signal and multiple interference signals. The signals arrive at the nodes as co-channel interferers. However, the antennas of the basestation appear as a distributed source to the nodes in a group near the basestation. Therefore, the nodes are able to distinguish between the signals sent from each antenna of the basestation. Each of the nodes is further operable to transmit a coherent repeated signal to a destination node such that the repeated signals collectively cancel out co-channel interference at the destination node. Therefore, the destination node receives a signal substantially free of co-channel interference.
In another embodiment, each group of nodes is divided into sub-groups of nodes. This division is based upon their ability to receive a first signal from the transmitter at a higher power level or a significantly different phase than these nodes receive a second signal from said transmitter. One subgroup coherently repeats to one destination node and another subgroup coherently repeats to another destination node.
Each node may also repeat the signal on multiple frequencies that are separated far enough apart to substantially eliminate selective frequency fading. This may be useful during the initial state of the network when there may be insufficient nodes to cooperate effectively.
These and other advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.